A battery is a device in which an electrochemical reaction, capable of producing energy, occurs spontaneously. Research in battery designs have been intensive technological endeavors for over five decades. Electronic devices, common in households, as well as observing and sensing systems with applications in various arenas motivate the development of powering systems with increased performance. Generally speaking, an electrochemical cell or galvanic cell couples two half-reactions to create a battery or power source. In one of these reactions a first compound reduces its oxidation state and in the other reaction a second compound oxidizes or losses electrons. The electron transfer can be harvested and used in electrical and electronics devices.
Various materials are known in the art for use as anodes for the fabrication of galvanic cells or batteries. When choosing a material to serve in a half reaction as part of a galvanic cell, the selected material should have an attractive oxidation potential. The oxidation potential is an indication of the achievable potential that the cell in which the selected material is used as an electrode is capable of providing, since the overall reaction potential is given by the sum of the potentials of the half reactions involved. Additionally, the sign of the oxidation potential and its magnitude provides insight on the spontaneity of the reaction. The table shown in FIG. 1 presents a list of standard oxidation potentials of several common anode materials in battery systems currently known in the art.
When fabricating practical battery cells, it is important to consider not only the standard oxidation potential but also the material's physicochemical characteristics. The molecular weight of the substance and its change in oxidation state will dictate the theoretical maximum specific energy that such a material can provide. The maximum specific energy is the energy per unit weight of the material. The theoretical energy density will be directly influenced by the material's density. The theoretical energy density is the energetic content per unit volume of the material.
Depending on the ultimate application, various parameters should be considered in the selection of a battery. Certain devices require batteries with a given potential output while drawing a specific current, while other devices require power outputs that are variable in nature and the batteries used for these devices should be able to provide a complex output profile.
The parameters that have been regarded as the most important to rate the performance of an electrochemical battery are the specific energy and/or the energetic density. The table in FIG. 2 illustrates several physicochemical properties of selected anode materials, including lithium, magnesium, aluminum and zinc, along with their theoretical energy content under standard conditions. The table in FIG. 2 also illustrates that lithium is the material with the highest energetic content per unit of mass. This explains why this chemical has been thoroughly investigated for battery development. Aluminum, due to its relatively low molecular weight for a charge transfer of three electron-mol per mol of substance and its low mass density has a higher energy density when compared to that of lithium. This is one of the reasons why aluminum has also been intensively investigated for the development of batteries. The table in FIG. 2 illustrates additional metals that present very attractive characteristics for electrochemical batteries, including magnesium and zinc, both of which have also been used in the past for developing battery systems.
In order to produce an electrochemical cell, a cathode half reaction is coupled to an anode reaction. The cathode reagent should be an oxidizer that is able to reduce the anode material. The table of FIG. 3 illustrates some common oxidizer reactions that have been used for electrochemical batteries that are currently known in the art.
Recent progress in the development of electrochemical batteries encompasses the use of novel materials that can serve as cathodes or anodes. Other types of galvanic cells have also been thoroughly investigated. In some cases the reagents are freshly introduced in the galvanic chamber containing the cathode and the anode for continuous power output. When reagents are utilized to replenish the function of either one of the electrodes, the cell is generally termed as a semi-fuel cell. When reagents are involved in both cathode and anode reactions a fuel cell is constructed. The oxygen reduction in the table of FIG. 3 is a half reaction commonly known in semi-fuel and fuel cells. Rechargeable batteries are another alternative that has been investigated in the art. The last two reactions in the table of FIG. 3 are examples of half reactions used in cells of rechargeable batteries. In general, regardless of the type of battery several issues should be considered, including safety, prevention of alternate reactions of the reagents and cost effectiveness. Regarding safety, it is important that the stored reagents and the products generated during the electrochemical reaction are safe and preferably amiable to constructing environmentally friendly devices. Additionally, it is important that the reagents do not follow alternate reactions, and if they do follow alternate reactions, that they are beneficial for the overall power system. An example of a beneficial alternate reaction can be found in the Lecanchle's cells that are known in the art. In the Lecanchle's cells, the hydrogen that is released in the cathode reaction, which is the first reaction illustrated in the table of FIG. 3, reacts with Mn02 and no interference is found in the cathode process. Also, it is important that the reagents and electrodes utilized in the electrochemical cell allow for the fabrication of a cost effective cell.
Many electrochemical battery systems are known in the art. A list of the reported galvanic cells that have appeared in literature can be found in the Handbook of Batteries, 3rd Edition, by D. Linden and T. B. Reddy, which is incorporated herein by reference. The table illustrated in FIG. 4 has been compiled from the Handbook of Batteries reference. The table shown in FIG. 4 illustrates selected battery systems as an illustration of available commercial systems based on active anode and cathode materials, including 02, but not air (electrolyte not included). The values listed are for single cell batteries based on the identified design and at discharge rates optimized for energy density using midpoint voltage.
The table shown in FIG. 4 includes primary batteries, those cells that are designed to be on the shelf and produce energy when in use and be disposed of after their useful life, in addition to secondary batteries, rechargeable batteries and fuel cells. An additional type of electrochemical cell known in the art is a reserve battery. A reserve battery requires activation operations that will close the circuit and start the production of energy “on-demand”. The activation operation could encompass events such as the introduction of electrolyte or the melting of substances to induce the conduction of ions responsible for the charge transfer between the anode and the cathode.
It is known in the art that aluminum, as well as magnesium and zinc, have been coupled with a very high number of available oxidizers, including oxygen from the air to form electrochemical cells. The table of FIG. 5 illustrates some of the solutions that are currently known in the art utilizing aluminum anodes. In spite of recent advances in these arenas, batteries utilizing these metals have not been successful in wide-spread commercial products primarily due to anode inefficiencies as well as unexpected polarization of the anodes.
Accordingly, what is needed in the art is an improved electrochemical battery that is safe, efficient and economical.